New to labview

[johnsold]

jayberns,

That card has 100 kS/s maximum sampling rate. It is completely unsuitable for the data rates you have mentioned.

If your maximum signal frequency is 10 MHz, then the Nyquist criterion states that you must sample at least twice that rate, or 20 MS/s. If the signal at 10 MHz is modulated or varies in magnitude quickly, a higher sampling rate might be required.

I would suggest that you need to do some careful specifying to determine the characteristics of the signal you want to measure and the types of measurements you want to make. Then you can start looking at the kinds of hardware and software you will need. Based on what you have indicated, you will likely need a high performance digitizer and may need to be careful with the program architecture to avoid memory allocation or performance bottlenecks.

Lynn

[Jeff_Spencer]

Hello again-

I have included a copy of my modified air valve control vi. I was wondering if anyone could/would take a look at it and tell me if I am going in the right direction with it. I am trying to operate a ratcheting brake lever with Lab View. In order to do this I need to time delay 2 air cylinders. The first cylinder actuates the lever, when it turns off the second air cylinder pushes the release button and allows the first cylinder to retract. I need to incorporate a load cell a physical counter as well, and then log everything to a data file (excel) at a given interval. Any help would be great. Thank you!!

[RavensFan]

Jayberns,

You highjacked the thread.  PLEASE START A NEW ONE!

Jeff,

Do you need any syncrhonization betweem the two digital out lines.  Do they need to operate simultaneously, or with a relative delay?  You need to have a clear task after your loop for the lower DAQ VI's.  You may need to create only a single task for both digital out lines.  Sometimes separate tasks will generate errors that the resource is already in use if they try to execute at the same time.  You'll have to see if you get errors when you run the code.  I don't know what circumstances lead to such an error.

[Jeff_Spencer]

Ravens Fan

I do need syncrhonization between the tow digital out lines, they need to be in complete syncrhonization with each outher, they have to operate in this order: # 1 off, the # 2 on, and vise versa. I did try to include a clear task after the loop for the lower DAQ vi, but when I included it, the lines were broken, and I wired it in just as the upper loop was wired. How would I create a single task for both digital lines? It did appear that the upper task would operate just a bit before the lower task, but that was with the higlight execution on.

[RavensFan]

You should be able to set multiple channels in the task ID.  So for line 0 and line 1 it would look like  Dev1/port0/line0,Dev1/port0/line1  or Dev1/port0/line0:1  I think there are many different ways for the syntax.  The DAQmx writes would have to be come N lines 1 point and you would need to wrie in an array of booleans.  You probably would need to wire the 4 or more DAQmx writes such as FT, TF, TT, TF, FF and calculate the appropriate amount delay times for each to allow a delay between the 2 lines, but allow for the appropriate ON and OFF times for each channel.

You may want to look at a state machine architecture with 5 states.  Chan 1 ON, Chan 1 Off, Chan 2 On, Chan2 off, and wait.  You could keep track of the current status of the digital outs.  After the appropriate amount of time, you could go from Wait to Chan 1 On and do that by taking the current state, setting the 1st boolean to True and writing the two booleans to the DAQmx write.  Go to the Wait state.   If you need absolute simultaneous On or Off create 2 more states  Both ON and Both OFF, where you write TT and FF.

This architecture would give you the most flexibility to be able to change the sequencing or timing as necessary

[jayberns]

Ok... I wish somewone could help me on this.. Base on my program ryt now, I could measure around 200 k Hz accurately..

[RavensFan]

Jayberns.

Listen carefully.   START A NEW THREAD!  Your topic has nothing to do with Jeff's questions.  He is the one who started this thread.  Your conversation is just creating noise.

[Jeff_Spencer]

I understand the logic in my program, (mine is the portion with the 4 loop and timing on/off for two air valves) and it works for what I need it to do, but I am trying to add to mine with the logging, load cell read, and the switch count that another programmer built, and I am getting LOST. If someone could take a look at this code and can tell me where I am going wrong, please do. I can't get it to count, and it doesn’t log correctly either. I have yet to connect a load cell at this point so I don't know if that works or not. Feel free to change any code you like and repost it if that can help out. Thank you.

[Donovan_B]

Hi Jeff,

When you say that the VI does not log correctly, what about the logging is incorrect?  Does it record the wrong values, not enough values, etc.?  Also, what does the Current Path.vi do?  Since it is not included, the VI will not run without removing it from the block diagram.

I also don't see where the "Counter" variable is ever written.  I see that it is read in the logging section of the code, but it does not seem to ever be written.  Is it written from another VI somewhere?  This could be why the logging is incorrect.

[Jeff_Spencer]

Donovan B

When you say that the VI does not log correctly, what about the logging is incorrect? Does it record the wrong values, not enough values, etc.?

The vi starts running the air valve as soon as you hit run. I want to be able to enter in the valid info into a screen before the valves start cycling. I know it needs a a sequence structure to do this, but I am not sure how to make it work in this mannor.

Also, what does the Current Path.vi do? Since it is not included, the VI will not run without removing it from the block diagram.

Current path is intented to bring in the values of load cells when the program is run, not sure that works correctly.

I also don't see where the "Counter" variable is ever written. I see that it is read in the logging section of the code, but it does not seem to ever be written. Is it written from another VI somewhere? This could be why the logging is incorrect.

I think you are correct in that the "Counter" cariable is not written. I was thinking "Count out" was doing that, but like I said new to Labview. Let me try to put something in where it will write it. Sorry it has taken so long to get back to this, busy in the lab running tests.